1. Field of the Invention
The present invention relates to the field of communications, and more particularly, the present invention relates to a mechanism for acquiring an ultra wideband signal.
2. Background Art
An impulse radio system typically includes an impulse radio transmitter for transmitting an impulse signal and an impulse radio receiver for receiving the impulse signal. An exemplary impulse signal includes a train of impulse signal frames each including one or more impulses. The transmitter can pulse position modulate the impulses within the impulse signal frames based on a modulating signal, and then transmit the impulse signal frames to the receiver.
The impulse radio receiver receives the impulse signal frames and associated received impulses transmitted by the impulse radio transmitter. In one known application, the impulse receiver coherently samples the received impulses to produce impulse samples. The receiver can use such impulse samples for subsequent signal processing relating to radar, position-locating, and communication applications, for example. However, before the impulse receiver can coherently sample the received impulses, it is necessary for the impulse receiver to determine a frame timing associated with the received impulses. That is, the impulse radio receiver must achieve frame synchronization (also referred to as proper frame alignment). For example, it is useful for the impulse receiver to determine when each received impulse signal frame begins and/or ends. Therefore, in an impulse radio capable of receiving an impulse signal including a train of impulse signal frames, there is a need to determine received impulse signal frame timing, such as a time when each impulse signal frame begins and/or ends.
Additionally, if the received impulse signal is coded (e.g., pulse position modulated based on a pseudo-random (PN) code), then the impulse radio receive must achieve code synchronization before it can coherently sample the received signal. Thus, there is also a need to provide code synchronization in an impulse radio capable of receiving an impulse signal including a train of code modulated impulse signals.
The impulse radio transmitter can transmit source information (i.e., digital data) to the impulse radio receiver. For example, the impulse transmitter uses the source information to pulse position modulate the impulses within the impulse signal frames, thereby producing information bearing symbols. The transmitter transmits the symbols (i.e., the impulse signal frames including the pulse position modulated impulses) to the impulse receiver. It is likely that the transmitter also codes the symbols as mentioned above prior to transmitting the impulse signal frames.
The impulse radio receiver receives the symbols transmitted by the impulse transmitter. Before the impulse receiver can demodulate the received symbols to recover the source information therein, the impulse receiver needs to recover a symbol timing associated with the received symbols. For example, the receiver needs to determine when each received symbol begins and/or ends. Once the receiver recovers such symbol timing, then the receiver can demodulate the received symbols to recover the data therein. Therefore, in an impulse radio capable of receiving symbols, there is a need to determine (or recover) received symbol timing, thereby enabling the impulse radio receiver to demodulate the symbols.
The impulse radio transmitter can pulse position modulate the impulses within the impulse signal frames based on different types of code sequences (codes), to produce a coded impulse signal. One type of code is a PN code used to channelize the impulse signal and/or combat relatively narrowband interference signals. These codes are relatively long (e.g., a code length of 1024, 2048 or 4096) for at least two reasons: first, so energy is spread across the frequency spectrum; and second, so a relatively large number of independent communication channels are provided.
In order to demodulate the coded impulse signal, the impulse radio receiver must be code synchronized with the impulse signal transmitter. Accordingly, there is a need to code synchronize the impulse radio receiver with the impulse radio transmitter.
It is typically beneficial to accomplish necessary requirements in fast and efficient manners that utilize reduced amounts of hardware to thereby increase throughput and/or reduce hardware costs. More specifically, it would be beneficial to satisfy each of the above discussed needs in fast and efficient manners that utilize reduced amounts of hardware. For example, it would be beneficial to achieve proper frame alignment in a fast and an efficient manner that utilizes reduced amounts of hardware. Further, it would be beneficial to recover received symbol timing in a fast and efficient manner that utilizes reduced amounts of hardware. Additionally, it would be beneficial to code synchronize an impulse radio receiver with the code of an impulse radio transmitter in a fast and efficient manner that utilizes reduced amounts of hardware. Still further, it would be beneficial if the same hardware could be used (or reused) to satisfy as many of the above needs as possible.